Comparative Study On The Guadalupian(Middle Permian)Conodont Biostratigraphy And Environmental Evolution Between South China And North America

The Guadalupian Epoch(Middle Permian)is one of the most critical intervals featured by a few unique major geological and biological events in global sense.These include:1)a critical transition of the supercontinent Pangea from the assembly to the dispersal stage.Accompanied with this transition were the massive eruptions of Emeishan basalt in South China.The 87Sr/86Sr ratio,which is related to oceanic spreading and continental weathering,decreased to the lowest point of the Phanerozoic in the Guadalupian.2)The Guadalupian Epoch represents a transition of paleoclimate from an icehouse of Late Paleozoic Ice Age toward a greenhouse stage.Global temperature gradually increased from Cisuralian(Early Permian)to Guadalupian(Middle Permian).3)Sea-level dropped to the lowest point at the end-Gaudalupian.Associated with the above mentioned major physical and geochemical changes are the dramatic environmental changes during the Guadalupian and the well-known pre-Lopingian biological extinction.Fundamental to understanding all geologcial and biological events among the Guadalupian is a high-resolution biostratigraphical,chemostratigraphical and geochronologic framework.Therefore,studies of the Guadalupian Series will offer important implications for understanding the tempo of biological events in the context of changing paleoclimates,ocean structures,land-sea configurations,and atmospheric chemistry.The Permian System has been officially divided into three different series,that is the Cisuralian,Guadalupian and Lopingian Series in ascending order which are respectively represented by the strata in the southern Urals,Russia;the Guadalupe Mts.in Texas,USA;and South China.The Guadalupian Series is defined by the FAD of the conodont Jinogondolella nankingensis at the base at the Stratotype Canyon section in the Guadalupe Mts.West Texas,USA and the FAD of the conodont Clarkina postbitteri postbitteri on the top at the Penglaitan section in the Laibin area,Guangxi,South China.Both South China and the Guadalupe Mts.possess the most complete Guadalupian Series since seawater withdrew from the most parts of Pangea Thus,a high-resolution intergrative time framework in both South China and North America is essential to work out their temporal and spatial relationship of all events occurred and realizes the global correlation of the Guadalupian Series.In this thesis,high-resolution conodont biostratigraphy and carbon,strontium and oxygen isotope chemostratigraphy from more than ten sections containing the strata from the uppermost Kungurian throughout the whole Guadalupian,including the Penglaitan,Lishihe,Changjianggou,Zhengpanshan and Pingdingshan sections in South China,and the Stratotype Canyon,Getaway Ledge,Nipple Hill,Patterson Hill and Gorden Bell sections in West Texas,USA,have been investigated in detail in order to realize the high-resolution correlation of the Middle Permian(Guadalupian)between South China and North America.Twenty-seven species/subspecies including two unidentified new species which belong to four families and ten genera are identified based on the sample population approach.They are Mesogondolella lamberti,Jinogondolella nankingensis,J.gracilis,J.aserrata,J.postserrata,J.shannoni,J.altudaensis,J.prexuanhanensis,J.xuanhanensis,J.granti,J.palmata,Clarkina postbitteri hongshuiensis,Hindeodus excavates,Hindeodus sp.,Ellisonia sp.,Neostreptognathodus cf.prayi,Neostreptognathodus sp.A,Sweetognathus adjunctus,S.bicarinum,S.subsymmetricus,S.iranicus hanzhongensis,S.fengshanensis,Sweetognathus sp.nov.A,Iranognathus paralanceolatus,Pseudohindeodus ramovsi,Pseudohindeodus sp nov.A and Pseudosweetognathus costatus.Based on these species,nine conodont zones in South China and six zones in West Texas are established and revised.They are Jinogondolella nankingensis,J.as errata,J.postserrata,J.shannoni,J.altudaensis,J.prexuanhanensis,J.xuanhanensis,J.granti,Clarkina postbitteri hongshuiensis zones in ascending order in South China and Jinogondolella nankingensis,J.aserrata,JJpostserrata,J.shannoni,J.altudaensis,J.prexuanhanensis zones in West Texas.The following new conclusions can be summarized:1)Rare specimens of Jinogondolella nankingensis with typical serration have been found from the horizons below the widely-perceived base of the Roadian Stage in both South China and Guadalupe Mts.,West Texas.However,its precise levels of the first appearances at the sections are difficult to be determined due to the rarity of specimens.It roughly locates in the upper part of the Chihsia Formation in South China and in the middle part of Cutoff Formation in West Texas.2)Jinogondolella aserrata is present at about 12 m below the GSSP mark of the Wordian Stage at the Getaway Ledge Section and the first occurrence of J.aserrata is not able to be revealed in Texas because the carbonate sequence is underlain by more than 100 m clastic sandstones which do not contain marine fossils.3)The conodont lineage and the first occurrence of Jinogondolella postserrata are also difficult to be determined in the basal part of the Capitanian Stage at the Nipple Hill Section because only half meter of the Capitanian is preserved and the overlying strata are not preserved there4)The topmost conodont zone in Texas is the J.prexuanhanensis Zone,USA,thus,the strata represented by the younger J.xuanhanensis,J.granti and Clarkina postbitteri hongshuiensis zones are missing or represented by evaporites without conodonts in the Delaware Basin,West Texas.Carbon isotope chemostratigraphy from the uppermost part of the Kungurian Stage through the entire Guadalupian Series has been investigated from the Penglaitan,Lishihe and Changjianggou sections in South China and a composite section in Texas,USA.?13Ccarb values are mostly around 4‰ in the upper part of Cisuralian and the whole Guadalupian except for several minor fluctuations in South China and Texas.The ?13Ccarb profiles are generally correlative in a long time scale between South China and Texas.However,an accurate correlation in view of high-resolution conodont zones is not possible.A distinct negative excursion is present in the Roadian in both South China and North America,which may offer global correlation potential.However,different patterns in the Wordian are also present between South and North America possibly due to subsequent diagenises and different sedimentary settings.The widely documented Kamra Event characterized by high positive ?13CCarb values is not well exhibited based on carbon isotope profiles in the South China and Texas.Strontium isotopes from the Kungurian to the topmost of Guadalupian have been established from the Penglaitan Section in South China and a composite section in West Texas,USA.The 87Sr/86Sr ratios are around 0.7075 in Texas and on the average higher than the values around 0.7071 in South China.The minimum of 87Sr/86Sr ratio,0.70693,is in the topmost part of Jinogondolella xuanhanensis Zone at the Penglaitan Section,which offers a potential point for global correlation.The 87Sr/86Sr ratio profile in West Texas shows a continuous decline through the whole Guadalupian until the last occurrence of conodonts,which suggests the Capitanian minimium of 87Sr/86Sr ratios is higher than the last occurrence of conodonts in the Guadalupian.Nevertheless,the general decline trends of 87Sr/86Sr ratios are largely correlative between South China and West Texas.High-resolution oxygen isotope profiles of conodonts are generally consistent between South China and Texas.Based on our new oxygen isotope data,there may be a cooling process in the Roadian in both regions.The temperature is relatively stable in the Wordian and early-middle parts of the Capitanian.However,South China was on the average about 4? higher than that in Texas,which suggests that the Delaware Basin in North America might be affacted by the coastal cooling currents along the western margin of Pangea.The ?18O curve shows a decreasing trend in the topmost part of the Capitanian at the Penglaitan Section,but this depletion is not revealed in Texas because either the strata are not complete or it may be in the evaporite deposits which are not available for strontium isotope analysis.